(a) Technical Field
The present invention relates to an apparatus for automatically punching and bonding membrane electrode assembly (MEA) materials for a fuel cell. More particularly, the present invention relates to an apparatus for automatically punching and bonding MEA materials for a fuel cell, which can automatically and continuously perform a punching process and a bonding process for the MEA materials by improving a conventional method in which a 5-layer MEA material is manually manufactured.
(b) Background Art
A fuel cell is an electricity generation system that does not convert chemical energy of fuel into heat by combustion, but electrochemically converts the chemical energy directly into electrical energy in a fuel cell stack. A fuel cell can be applied to the supply of electric power for small-sized electrical/electronic devices, for example, portable devices, as well as to the supply of electric power for industry, home, and vehicles.
At present, the most attractive fuel cell for a vehicle is a polymer electrolyte membrane fuel cell (PEMFC), also called a proton exchange membrane fuel cell, having the highest power density among the fuel cells. The PEMFC has a fast start-up time and a fast reaction time for power conversion due to its low operation temperature.
The PEMFC comprises: a membrane electrode assembly (hereinafter referred to as an MEA) including a polymer electrolyte membrane for transporting hydrogen ions and an electrode/catalyst layer, in which an electrochemical reaction takes place, disposed on both sides of the polymer electrolyte membrane; a gas diffusion layer (hereinafter referred to as a GDL) for uniformly diffusing reactant gases and transmitting generated electricity; a gasket and a sealing member for maintaining the airtightness of the reactant gases and coolant and for providing an appropriate bonding pressure; and a bipolar plate for transferring the reactant gases and coolant.
In a fuel cell having the above-described configuration, hydrogen as a fuel is supplied to an anode (also referred to as a fuel electrode or oxidation electrode), and oxygen (air) as an oxidizing agent is supplied to a cathode (also referred to as an air electrode, oxygen electrode, or reduction electrode).
The hydrogen supplied to the anode is dissociated into hydrogen ions (protons, H+) and electrons (e−) by a catalyst of the electrode/catalyst layer that is provided on both sides of the electrolyte membrane. At this time, only the hydrogen ions are transmitted to the cathode through the electrolyte membrane, which is preferably a cation exchange membrane, and at the same time the electrons are transmitted to the anode through the GDL and the bipolar plate, which serve as conductors.
At the anode, the hydrogen ions that are supplied through the electrolyte membrane and the electrons that are transmitted through the bipolar plate meet the oxygen in the air supplied to the anode by an air supplier and cause a reaction that produces water.
Due to the movement of hydrogen ions caused at this time, the flow of electrons through an external conducting wire occurs, and thus a current is generated.
The electrode reactions in the polymer electrolyte membrane fuel cell can be represented by the following formulas:Reaction at the anode: 2H2→4H++4e−Reaction at the cathode: O2+4H++4e−→2H2OOverall reaction: 2H2+O2→2H2O+electrical energy+heat energy
As exemplified in the above reaction formulas, a hydrogen molecule is dissociated into four hydrogen ions and four electrons at the anode. The generated electrons move through an external circuit to generate a current, and the generated hydrogen ions move to the cathode through the electrolyte membrane to perform a reduction electrode reaction.
The fuel cell stack is formed by repeatedly stacking a plurality of unit cells, and each of the unit cells has a structure in which the bipolar plate, the GDL, and the MEA are stacked.
In manufacturing the fuel cell stack, the components of the unit cell such as the bipolar plate, the GDL, and the MEA are repeatedly stacked. In a 5-layer MEA material, the GDLs and the MEA are stacked in a 5-layer structure, and the bipolar plates are stacked alternately and assembled.
The 5-layer MEA material has a structure in which two GDLs are additionally bonded to a 3-layer MEA, including an electrolyte membrane and electrode catalysts (a cathode catalyst and an anode catalyst), which will be described in more detail with reference to FIGS. 1 and 2 below.
As shown in FIG. 1, a cathode catalyst 2 and an anode catalyst 3 are preferably bonded on the top and bottom sides of a Nafion membrane (a suitable electrolyte membrane) 1 to prepare a 3-layer MEA, and a sub-gasket 4 is bonded to the top and bottom sides of the Nafion membrane 1, except for the catalyst portions, to facilitate the handling of the 3-layer MEA.
In the preparation of the 3-layer MEA to which the sub-gaskets 4 are bonded, the portions corresponding to manifolds are punched to form openings 6 as shown in FIG. 2. Preferably, the GDL 7 is bonded to the top and bottom of the 3-layer MEA with the manifold openings 6 at high temperature and high pressure, thus forming a 5-layer MEA material 8.
A conventional method of forming the 5-layer MEA material 8 includes fixing the 3-layer MEA 5 including the sub-gaskets 4 on a manifold punch press, manually operating the press to punch the manifolds openings 6, removing a backing sheet attached to protect the catalyst layer, transferring the resulting 3-layer MEA 5 to a hot press device, stacking the GDL 7, the 3-layer MEA 5, the GDL 7 in the sequential order, and operating the hot press device, thus completing a final 5-layer MEA material 8.
In this example, since the hot press device bonds the 3-layer MEA and the GDLs under high temperature and high pressure conditions, the hot pressing process requires considerable time and, for example, the process of punching the manifold openings on the 3-layer MEA and the hot-pressing process of stacking and bonding the GDLs is not automated.
Accordingly, during the punching process, the manifold punch press is manually operated and, as such, the resulting 3-layer MEA materials are manually transferred to the hot press device for the hot-pressing process by a worker. After stacking the GDLs and the 3-layer MEA, the hot press device is also manually operated to perform the hot-pressing process. Accordingly, it takes considerable time to perform the punching process and the hot-pressing process.
During the manual bonding process as described above, the supply of the finished 5-layer MEA materials is not generated according to a smooth or regular process, thus an automatic stacking device is operated only after a necessary amount of the 5-layer MEA materials is gathered to complete the fabrication of the fuel cell stack.
Furthermore, the performance of the fuel cell stack as well as the working time may be varied according to the workers who perform the stacking process, and thus waste of manpower, inefficient production, a difficult in mass production, and the like may occur.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.